Coions, in addition to counterions, interact with polyelectrolytes in solution. The coion-polyion interaction in solution will be studied experimentally, (1) by comparing the specific interactions of several anions with a given polyelectrolyte, (2) by determining the influence of the charge density of the polyelectrolyte on its interaction with coions, and (3) by determining the concentration dependence of the interaction. Because they contain different ionizable groups, the sodium salts of iota-carrageenan, algin and DNA will be used. The anions chosen are Cl minus, I minus, NO3 minus, CN minus, SO4 minus 2, CO3 minus 2, and PO4 minus 3. The experimental techniques to be employed are the emf method utilizing specific ion electrodes and the capillary method for the self diffusion of the anion.